C#でPDFファイルから画像を抜き出す 導入編 (iTextSharp)

using System;
using System.Collections.Generic;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
using iTextSharp.text.pdf;


namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            PDFtoImage(@"C:\test.pdf", @"C:\images\");
        }

        static void PDFtoImage(string pdfName, string imgFolder)
        {
            var imgName = Path.GetFileNameWithoutExtension(pdfName);

            var pdf = new PdfReader(pdfName);
            var images = new List<PdfObject>();
            int n = pdf.NumberOfPages;
            for (int i = 1; i <= n; i++)
            {
                PdfDictionary pg = pdf.GetPageN(i);
                CollectImage(pg, images);
            }

            for (int i = 0; i < images.Count; ++i)
            {
                var obj = (PRIndirectReference)images[i];
                var pfdStream = (PRStream)pdf.GetPdfObject(obj.Number);
                byte[] bytes = PdfReader.GetStreamBytesRaw(pfdStream);

                var name = string.Format("{0}{1}_{2}.jpg", imgFolder, imgName, i);
                File.WriteAllBytes(name, bytes);
            }
        }

        static void CollectImage(PdfDictionary dic, List<PdfObject> images)
        {
            var res  = (PdfDictionary)PdfReader.GetPdfObject(dic.Get(PdfName.RESOURCES));
            var xobj = (PdfDictionary)PdfReader.GetPdfObject(res.Get(PdfName.XOBJECT));
            if (null != xobj)
            {
                foreach (PdfName name in xobj.Keys)
                {
                    PdfObject obj = xobj.Get(name);
                    if (obj.IsIndirect())
                    {
                        var tg = (PdfDictionary)PdfReader.GetPdfObject(obj);
                        var type = (PdfName)PdfReader.GetPdfObject(tg.Get(PdfName.SUBTYPE));
                        if (PdfName.IMAGE.Equals(type))
                        {
                            images.Add(obj);
                        }
                        else if (PdfName.FORM.Equals(type))
                        {
                            CollectImage(tg, images);
                        }
                        else if (PdfName.GROUP.Equals(type))
                        {
                            CollectImage(tg, images);
                        }
                    }
                }
            }
        }
    }
}